Wireless communication devices, such as cellular telephones, two-way radios, personal digital assistants (PDA), pagers, personal computers (PC), laptop computers, home entertainment equipment, etc., typically include a built-in radio transceiver (i.e., transmitter and receiver) for communicating directly or indirectly with other wireless communication devices. Each transceiver is configured to operate in one or more frequency bands using one or more communication standards. Examples of communication standards include, but are not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), wideband CDMA, Time Division Duplex (TDD), and/or variations thereof.
Manufacturers of wireless communication devices usually test the device transceivers for proper operation in each applicable frequency band for each applicable communication standard before shipping the wireless communication devices to end users. For example, common transceiver tests include error-vector magnitude (EVM) for transmitter modulation accuracy, bit error ratio (BER) or signal to noise and distortion (SINAD) for the receiver sensitivity in the presence of signals and noise, and spectral mask for the transmitter adding unwanted signals. Wireless communication devices are typically tested by a transceiver testing device that includes a test transceiver for communicating with the wireless communication device to make the various measurements of the wireless communication device.
In order to effectively test transceivers in different frequency bands and/or for different communication standards, the test transceiver should be designed for general testing of all potential frequency bands and communication standards. Thus, the test transceiver should be able to accommodate testing in different transmit and receive frequency bands and testing in the same frequency band for both transmit and receive. Modem communication standards can utilize time division multiple access (TDMA), frequency division multiple access (FDMA), time division duplex (TDD), code division multiple access (CDMA), or combinations of these standards. As a result, many new systems have large transient signals. In systems employing large transient signals (e.g., WCDMA signals and TD-SCDMA signals), transmitters will operate a power levels that are significantly higher than receivers. Therefore, when testing transceiver devices that use the same frequency band for transmit and receive, such as a system utilizing time division duplex (TDD) on the same frequency, there must be sufficient isolation between the test transmitter and test receiver to avoid overloading the test receiver.
One solution to avoiding receiver overload is to use a high isolation switch module at the front end of the test transceiver to switch the antenna between the transmitter and the receiver. However, these switch solutions rely on precise timing, which may not be possible when testing transceiver devices designed for use in asymmetric transmit/receive systems where the bandwidth timeslots are not shared equally between transmit and receive modes. In addition, it is difficult to obtain high isolation at RF frequencies. Another solution to avoiding receiver overload is to use multiple receivers programmed to receive different power levels. However, the extra hardware required for each additional receiver undesirably increases the cost and complexity of the transceiver testing device. Therefore, what is needed is a transceiver testing device that provides sufficient receiver overload protection when testing both symmetric and asymmetric systems without requiring additional receivers.